Your girlfriend is probably ineligible for
any UK visa.
She can visit the UK for up to 6 months at a time without a visa. However, she would not be permitted to work during that time unless she held a temporary work permit. Such a permit must be applied for by her potential employer
before she travels and must not be valid for longer than 6 months.
For a stay of longer than 6 months your girlfriend would require a relevant visa which has to specify the purpose of the visit. Probably the only purpose that might be considered is 'work'. Such visas are only issued on a points-based system and I doubt that your girlfriend would qualify.
Start here for further information:
http://www.ukvisas.gov.uk/en/
Chris